Electrical, in particular, however, electronic measuring, control, regulating, and switch circuits, and also for telecommunication arrangements and assemblies are susceptible to transient over-voltages, commonly called power surges, such as those than can occur through atmospheric charges, or also through switch activity or short circuits in energy supply networks. This susceptibility has been used increasingly in electronic components, in particular, transistors and thyristors; above all, integrated circuitries are increasingly endangered in great numbers by transient power surges.
Electrical circuits work with the specified voltage, the rated voltage, normally failure-free. This is not the case when power surges occur. Power surges are all voltages, which lie above the upper tolerance limit of the rated voltage. In this regard, also the transient power surges are counted, which based on atmospheric charges, however, also by switch activity or short circuits, can occur in energy supply networks and can be coupled galvanically, inductively, or capacitively in electric circuitry. In order to protect electrical or electronic circuitry against power surges, in particular, electronic measuring, control, regulating, and switching circuits, as well as telecommunication units and assemblies, where also they are used, power surge protection elements have been developed and have been known for more than 20 years.
Certain surge protection arrangements include at least one spark gap, which with a determined surge activates the operating voltage and therewith prevents power surges from occurring in the circuitry protected by a power surge protection element that are greater than the operating voltage of the spark gap.
With air breakdown spark gaps, generally a breakdown spark gap is meant; included, then, also is a breakdown spark gap, with which not air, but a different gas, is provided between the electrodes. In addition to power surge protection elements with an air flashover spark gap, power surge protection elements with an air flashover spark gap are provided, with which upon activation, a creepage charge occurs.
Power surge protection elements with an air breakdown spark gap, in contrast with power surge protection elements with an air flashover spark gap, have the advantage of a higher surge current carrying capacity, however, the disadvantage of a higher—and also not rather constant—operating voltage. Thus, already different power surge protection elements are proposed with an air breakdown spark gap, which with reference to the operating voltage, have been improved. In this manner, in the area of the electrodes or the active air breakdown spark gap between the electrodes, were realized in various manners with the sparking or ignition aids, for example, such between the electrodes, at least one creepage charge releasing ignition aid was provided, which at least partially projects into the air breakdown spark gap, is designed as graduated, and is made of plastic (compare, for example, the German disclosure documents 41 41 681 or 44 02 615).
The previously mentioned ignition or sparking aids with the previous power surge protection elements can be designated as “passive sparking aids”, “passive sparking aids” because they themselves do not activate “actively”, rather only by means of a power surge, which acts on the main electrode.
In German published patent document 198 03 636, likewise a power surge protection element with two electrodes is described, with an active air breakdown spark gap between the two electrodes and an ignition or sparking aid. With this power surge protection element, the sparking aid, in contrast to the previously mentioned types, forms a creepage charge releasing sparking aid as an “active sparking aid”, namely in that in addition to the two electrodes—here designated as main electrodes—two more sparking electrodes are provided. These two sparking electrodes form a second air breakdown spark gap, serving as an ignition spark gap. With this power surge protection element, an ignition circuit belongs to the ignition aid outside of the ignitions spark gap with an ignition switch element. Upon contact of a power surge to the power surge protection element, the ignition circuit with the ignition switch element provides for an activation of the ignition spark gap. The ignition spark gap or the two ignition electrodes are arranged with reference to the two main electrodes such that, thereby, it has activated the ignition spark gap, the air breakdown spark gap between the two main electrodes, called the main spark gap, activates. The activation of the ignition spark gap leads to an ionization of the air provided in the air breakdown spark gap, so that, abruptly, after activation of the ignition spark gap, then also the air breakdown spark gap between the two main electrodes, that is, the main spark gap, activates.
With the previously described embodiments of power surge protection elements with ignition aids, the ignition aids lead to an improved, specifically lower and more constant operating voltage.
With surge protection arrangements of the type discussed—with or without an ignition air—upon ignition of the air breakdown spark gap a low-impeded connection arises between the two electrodes. Via this low-impeded connection, first the lightning current to be dissipated flows. With an adjacent network voltage, however, an undesired network sequence current follows via this low-impeded connection of the surge protection arrangement, so that one is anxious to extinguish the arc as quickly as possible after the completed arresting process. One possibility for achieving this goal is to enlarge the arc length and therewith, the arc voltage.
One possibility for extinguishing or canceling the arc after the arresting process, namely, to enlarge the arc length and therewith the arc voltage, is realized with the surge protection arrangement, as is described in German published patent document 44 02 615. The surge protection arrangement described in this document has two narrow electrodes, which, respectively, are angularly formed and which each have a spark horn and a connection leg angled therefrom. In addition, the spark horns for the electrodes are provided with a bore in the regions bordering the connection leg. The bores provided in the spark horns of the electrodes sees to it that in the moment of the activation of the surge protection element, that is of the ignition, the arisen arc is “put into motion”, that is, diffused away from its formation position. Since the spark horns of the electrodes are arranged V-shaped relative to one another, the gap to be bridged over from the arc, upon diffusing out of the arc, enlarges, whereby also the arc voltage increases.
A further possibility for extinguishing the act after the arresting process exists in the cooling of the arc by means of the cooling action of insulation walls, as well as the use of gas-emitting insulation. In this manner, an intense flow of the extinguishing gas is necessary, which requires a high constructive expense.
If the arc is extinguished in surge protection arrangements of the type discussed, then first, the low-impeded connection between the two electrodes is interrupted, the space between the two electrodes, that is, the region of the air breakdown spark gap, is almost completely filled with plasma, however. By means of the existing plasma, however, the operating voltage between the two electrodes is lowered, such that it can result in a renewed ignition of the air breakdown spark gap already with an adjacent operating voltage. This problem occurs particularly, then, when the surge protection arrangement has an encapsulated or half-open housing, since then, a cooling or escape of the plasma is prevented by the essentially closed housing.
In order to prevent a renewed ignition of the surge protection arrangement, that is, the air breakdown spark gap, different features have been proposed up to now, in order to drive away or cool the ionized gas clouds from the ignition electrodes. In this connection, constructively expensive labyrinths and cooling bodies are used, whereby the manufacture of the surge protection arrangement is made more expensive.
In German published patent document 100 40 632, a surge protection arrangement is described, in which a renewed activation of the air breakdown spark gap is prevented after the arresting process, which can be realized constructively simply. With this surge protection arrangement, it operates with a main spark gap, with an ancillary spark gap, and with a housing accommodating the main spark gap and the ancillary spark gap, whereby the main spark gap has a first main electrode, a second main electrode, and an existing or active air breakdown spark gap between the main electrodes, and upon ignition of the air breakdown spark gap, an arc arises between the first main electrode and the second main electrode. The ancillary spark gap has a first ancillary electrode, a second ancillary electrode and a second air breakdown spark gap between the ancillary electrodes. An ignition of the two air breakdown spark gaps lead to an ignition of the first air breakdown spark gap, whereby the second ancillary electrode, via at least one impedance, is directly or indirectly connected with the second main electrode.
U.S. Pat. No. 5,436,608 describes a surge protection element, in which the operating voltage, or ignition voltage, is preset by the geometric dimension of the silicon chip. The ignition voltage is determined by the height of a projection on the silicon chip, the projection being located in an insulated manner between an electrode and the silicon chip. This arrangement has the disadvantage that the operating voltage is accomplished through accurate configuration of the height of the projection. This requires high accuracy of manufacture; subsequent change of the operating voltage is not possible. Moreover, the insulating film required for this device can be damaged or destroyed when a power surge is discharged, as a result of which the surge protection element would be changed in its operating voltage to such an extent that it would no longer be functional.
Document JP 09266052 from Patent Abstracts of Japan describes a surge protection element, which is composed of two opposite electrodes having a special shape, and in which a capacitive impedance, in particular a capacitor and a resistor, is connected between the electrodes. However, this arrangement is only able to discharge smaller surges, which do not yet produce any spark between the opposite electrodes. To ignite the spark gap between the opposite electrodes, the ignition voltage of the spark gap must be reached or exceeded.
German patent document DE 19510181 C1 describes a surge protection element, in which a first spark gap is used to trigger the flashover at the second, that is, the main spark gap. In this context, the operating voltage of the first spark gap is set by the electrode spacing of the first spark gap and an impedance connected in series thereto. In this arrangement too, an accurate dimensioning of the electrode spacing of the first spark gap is necessary for the adjustment of the ignition voltage.
French patent document FR 1105378 A describes a surge protection element including a main spark gap and a parallel ancillary spark gap with a capacitance. A capacitance is connected to the ancillary spark gap, the geometric arrangement being designed in such a manner that an ignited ancillary spark gap will not ignite the main spark gap. Here, the ancillary spark gap is intended to discharge smaller surges; the main spark gap igniting automatically without ignition aid and only when a larger surge occurs.